COVER GP-VALVE MECHANISM 3555091 - Caterpillar

Illustration 20 g02783242
Solenoid to ECM connections for the solenoids that are used in the implement control systemNote: As part of the standard implement control system logic, engine torque is limited to 1100 rpm by the implement hydraulic pump load on the engine. This feature will limit the proportional current for lift and tilt commands when nearing a mechanical stop position.Implement Pilot Supply Solenoid Valve
The Implement ECM controls the operation of the Implement Pilot Supply Solenoid Valve with a 24 VDC ON/OFF output.The status of the Hydraulic Lockout Switch, will determine when the ECM will energize or de-energize the solenoid.When the switch is in the UNLOCK position with the engine OFF, the Pilot Supply Solenoid will only be energized if the operator commands implement movement by moving a lever or the joystick. When energized with the engine OFF, pilot accumulator pressure pilot will be supplied to the implement control valve.When the engine is operating and the switch is in the UNLOCK position, the ECM will energize the Implement Pilot Supply Solenoid continuously. The energized solenoid will allow system pilot oil pressure to be supplied to the implement control valve. If the ECM detects an abnormal condition in the solenoid circuit, the solenoid will be de-energized.When the switch is in the LOCK position, the ECM will de-energize the ON/OFF output for the Implement Pilot Supply Solenoid. Pilot oil will be blocked from the implement control valve.In addition, the ECM will disable all proportional solenoid outputs. Implement control will be disabled.If the key start switch is in the ON position, Hydraulic Lockout Switch is in the OFF position, and the engine is not in operation, the ECM will de-energize the Implement Pilot Supply Solenoid. Pilot pressure will remain in the pilot accumulator. Under these conditions, an implement operator command will result in the ECM energizing the solenoid valve in order to allow valve spool movement.The resistance of a good solenoid coil is 33.8 3 ohms at 20° C (68° F). Resistance is slightly affected by operating temperature. Resistance will increase as temperatures increase.Implement Control Solenoid Valves (Raise, Lower, Tilt Back, Dump) - Auxiliary Third Function Solenoid Valves (Port A, Port B)
To control the proportional solenoid valves in the electrohydraulic implement control system, the Implement ECM will use PWM driver circuits for each solenoid.The ECM will use a Pulse Width Modulated (PWM) signal to energize the solenoids. The ECM will vary the duty cycle of the PWM signal in order to control the amount of electrical current that is sent to the proportional solenoids. As the duration of the high signal increases, the percentage of the duty cycle and the amount of electrical current in the circuit will increase.A PWM duty cycle is the percentage of time that the signal is "High" compared to the amount of time that the signal is "Low" for a complete cycle.For the control of the implement system solenoid valves, the ECM will apply a current amount that corresponds to the input signals from the operator controls.